Can some one tell me how to solve any of these precal equations?

I am trying to pass an online test to get into a college calculus class, and I took precal like three years ago. These are the questions I got wrong and I need to figure out why. I have the answers, but I don’t understand how to reach them mathematically.

Also, I’ve written equations in a sort of long form because I don’t have proper symbols, so exponents are written as x^y, like on a calculator.

Thanks to anyone who’ll help me with this, I really need it.

1. Find the value of the side of a square whose diagonal is known as ‘a’. (Answer: [a times (square root of 2)]/2)

2. evaluate: sin of pi/6 (Answer: 1/2)

3. A population has P(t)=155063e^(0.14t) individuals, how man days (t) are necessary for the population to reach 1,000,000? (Answer: 13.3137)

4. distance of a car is represented by s=t^2+2t Find the average velocity from t=1 to t=5. (Answer: 12ft/sec)